This work aims at providing a more detailed understanding of the function and mechanism of the enzyme DNA ligase from Escherichia coli. This objective will be approached by synthesizing several NAD ion analogues in which the oxygen atom attached to the 5'-carbon atom of the adenylic acid moiety of NAD ion has been substituted by electronegative groups ranging from sulfur through nitrogen to the methylene group. In addition, the substrate group specificities of the enzyme from mouse L-cells will be examined. Finally, for comparative purposes, the enzyme RNA ligase from T4-infected E. coli will be purified in large amounts and characterized both as a protein and as an enzyme. Reaction conditions will be sought which will allow this enzyme to be used in the synthesis of chemical amounts of deoxyribonucleotides of defined sequences. BIBLIOGRAPHIC REFERENCES: Bedows, E., Wachsman, J.T., and Gumport, R.I., Biochem. Biophys. Res. Commun. 67 1100-1107 (1976), "Absence of Detectable RNA Ligase Activity in Eukaryotic Cells."